JP2767425B2 - Replacement element chip mounting method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for mounting a multi-chip contact image sensor in a facsimile reading apparatus, and a conversion element chip such as a display element, a light emitting element, and a printing element.

(Prior Art) A die bonder is conventionally used when a conversion element chip such as a light receiving element is die-bonded to a substrate in a multi-chip contact image sensor or the like.

As shown in FIG. 8, in the method using the die bonder, the substrate 4 is mounted on the stage 2, while the light receiving element chip 6 is held by the collet 8 and the chip 6 is aligned with the substrate 4. The chip 6 is bonded onto the substrate 4 with an adhesive 10.

However, the positioning accuracy of the chip 6 by the die bonder depends on the processing accuracy and the transfer accuracy of the stage 2 and the collet 8 of the die bonder. In the die bonder, since the position of the chip 6 is determined based on the outer shape of the chip 6, the influence of the dicing accuracy of the chip 6 is also exerted.
The dicing accuracy is usually about ± 5 μm. For this reason,
The die bonding accuracy of a chip using a die bonder is limited to about ± 20 μm.

As a bonding method for semiconductor integrated circuit device chips, there is a flip chip method. Since the flip chip method is a solder reflow method, if the means for controlling the amount of solder is fixed, the position of the chip is self-corrected by the surface tension of the bumps, so that the positioning accuracy of die bonding is known to be excellent. Have been. The flip chip method is generally used in a face-down method. Since the surface on which an element such as a transistor is formed and the surface on which a bump is formed are the same surface, it is easy to position the bump with respect to the element.

However, in the case of the conversion element chip, if an attempt is made to adopt the flip chip method, bumps for die bonding are formed not on the front surface on which the conversion element is formed but on the back surface side. Therefore, it is difficult to form a bump at an accurate position. For example, as shown in FIG. 9, even if the bump 13 is formed on a line that is shifted from the position on the predetermined line by an angle θ, the bonding accuracy is greatly deteriorated.

(Object) It is an object of the present invention to provide a method for die bonding a conversion element chip such as a light receiving element chip with high accuracy by using a flip chip method.

(Configuration) The present invention includes the following steps (a) to (d).

(A) From the surface of the wafer having the conversion element formed on the surface,
A step of forming an alignment mark based on the pattern of the surface by photolithography and anisotropic etching; (b) forming a resist on the back surface of the wafer and transmitting the X-ray through the wafer to form the alignment mark; Using a photolithography process to pattern the resist, (c) forming a bump using the resist pattern as a mask, and (d) cutting the wafer into chips. A step of bonding by flip-chip method on a substrate using bumps.

The bumps on the back surface for die bonding are aligned with reference to the alignment marks on the chip surface, and the alignment marks are aligned with reference to patterns such as conversion elements on the chip surface. Exactly aligned with the pattern. If die bonding is performed by flip-chip using the bumps, the position of the chip is self-corrected by the surface tension of the bumps, and highly accurate die bonding is performed.

 Hereinafter, examples will be specifically described.

FIG. 1 shows a semiconductor wafer 12 having light receiving elements formed on its surface.
5 shows a state in which the alignment mark 14 is formed from the surface of FIG.

The alignment mark 14 can be formed by performing selective etching by photolithography and anisotropic etching at an arbitrary position on the basis of the light receiving element pattern on the wafer surface. As the anisotropic etching, for example, wet etching using a mixed solution of hydrofluoric acid and nitric acid, or anisotropic dry etching can be used.

As shown in FIG. 2, the alignment mark 14 may be formed with a concave portion on the surface of the wafer 12 so that the thickness of the wafer 12 is made different between the inside and outside of the alignment mark 14. As shown in the figure, a hole reaching the back surface may be formed.

Next, a resist pattern is formed on the back surface of the wafer 12 by photolithography with reference to the alignment mark. In order to align the mask for forming the resist pattern, a resist 16 is formed on the back surface of the wafer 12 as shown in FIG. As shown in (B), the alignment mark 14 is detected based on the transmitted light intensity of the soft X-ray 18, and the position of the mark is used as a reference. The soft X-rays 18 may be transmitted from the back side of the wafer 12 as shown in the drawing, or may be transmitted from the front side.

After positioning the wafer 12 and the mask in this manner, the resist 16 is exposed, developed, and patterned.

A bump is formed on a portion of the back surface of the wafer 12 exposed by the opening of the resist 16, but in order to improve the adhesion between the bump and the wafer 12, the wafer 12 is formed before the resist 16 is formed.
For example, Cr or Ni may be formed on the entire back surface by vapor deposition or the like.

Solder bumps are formed using the resist pattern formed on the back surface of the wafer 12 as a mask. The bumps are formed by first forming Cr using a plating method, as is conventionally done.
Cu is formed thereon, and a solder layer is further formed.

FIG. 5 shows one chip 20 obtained by forming the solder bumps 22, removing the resist, and dicing the wafer. 24 is a bonding pad on the front side.

Wet back is performed to bring the bump 22 closer to a sphere. It is desirable that the shape of the bump be controlled so as to be spherical with a radius of about 60 to 70 μm.

Next, as shown in FIG. 6, the bumps 22 of the chip 20 are aligned with the pattern 28 of the substrate 26. The positioning at this time does not need to be highly accurate. Thereafter, the bump 22 is reflowed by heating and flowing the flux 30, and the position of the chip 20 is self-corrected by the surface tension of the bump 22, as shown in FIG. The arrow indicates that the chip 20 has moved due to the surface tension of the bump 22. The radius of the bump 22 is 60 to 70 μm
, The light-receiving element pattern on the surface is ±
Die bonding can be performed with an accuracy of about 10 μm or less.

After die bonding of the chip 20, the bonding pad 24 on the chip surface and the wiring on the substrate 26 are connected by, for example, a wire bonding method.

The present invention can be applied not only to a contact image sensor but also to a device that requires high-precision multi-chip mounting, for example, mounting of various conversion element chips such as an LED print head.

(Effect) In the present invention, an alignment mark is formed on the front surface of a wafer, X-rays are transmitted through the wafer, bumps are formed on the back surface with reference to the alignment marks on the front surface, and flip chips are formed using the bumps on the back surface. Since the die bonding is performed according to the method, the mounting can be performed with higher accuracy than when a die bonder is used, without depending on the dicing accuracy of the chip.

[Brief description of the drawings]

1 is a perspective view showing a state in which alignment marks are formed in one embodiment, FIGS. 2 and 3 are cross-sectional views showing alignment marks, respectively, and FIG. 4 (A) is an alignment in photolithography. FIG. 5B is a diagram showing a transmitted X-ray signal, FIG. 5 is a cross-sectional diagram showing a state in which the chip is cut after bump formation, and FIG. 6 is a diagram in which the chip is aligned on a substrate. FIG. 7 is a sectional view showing a state after bonding. FIG. 8 is a schematic view showing a mounting method using a die bonder, and FIG. 9 is a schematic plan view showing a flip chip method when a bump position is shifted. 12 ... wafer, 14 ... alignment mark, 16 ... resist, 18 ... soft X-ray, 20 ... chip, 22 ... bump, 24 ...
... bonding pads, 26 ... board, 28 ... board pattern,

Claims (1)

(57) [Claims] 1. A method of mounting a conversion element chip including the following steps (a) to (d). (A) From the surface of the wafer having the conversion element formed on the surface,
A step of forming an alignment mark based on the pattern of the surface by photolithography and anisotropic etching; (b) forming a resist on the back surface of the wafer and transmitting the X-ray through the wafer to form the alignment mark; Using a photolithography process to pattern the resist, (c) forming a bump using the resist pattern as a mask, and (d) cutting the wafer into chips. A step of bonding by flip-chip method on a substrate using bumps.